Valves, and especially sample valves may be used to simplify the extraction of samples from e.g. tanks, reactors and pipelines. Generally, a sample valve comprises a sample fluid inlet, a fluid outlet, a cleaning fluid inlet, a valve seat and an actuator arranged to set the valve to control a flow between the inlets and the outlet.
Especially in the food industry, there are strict requirements regarding the cleaning possibility of all surfaces that have been exposed to a product. Cleaning may be accomplished by hot steam being injected through the valve from the cleaning fluid inlet, past the valve seat and to the fluid outlet when the sample fluid inlet is closed off.
The operation of a sample valve requires a movement of one or several pistons arranged in the actuator of the valve, together or independently of each other, typically depending on an operation cycle. An operation cycle comprises essentially a closed position, an open position and a cleaning position. In the closed position, often referred to as a default position, any flow out of the sample fluid inlet is prevented. In the open position, the sample fluid inlet is open, allowing a sample fluid to be collected via the fluid outlet. In the cleaning position, a portion of the valve seat is exposed to allow cleaning thereof while any sample flow from the sample fluid inlet is still closed off. In the closed position, the portion of the valve seat that is exposed in the cleaning position is in direct or indirect contact with a piston that forms part of the actuator and/or is in contact with a sealing membrane that covers a part of the piston. By, in the cleaning position, exposing a part of the valve seat, residues may be removed by a flow of cleaning fluid supplied at the cleaning fluid inlet and flowing over the exposed part.
For effecting such cleaning it is known to provide the actuator with coaxially arranged, dual piston rods. The operation of the dual piston rods is controlled via three fluid supply inlets. This affects the complexity of the actuator and also the costs for manufacturing and maintenance.
The same problem is true for other types of valves as well, i.e. there is a general need for reducing complexity of and costs for manufacturing and maintaining a valve actuator, and in particular an actuator where one piston rod is coaxially arranged with another piston rod.